When the signals recorded on opposite sides of an optical disk are reproduced using a common optical video disc reproduction apparatus, it is necessary to remove the disc from the apparatus after the reproduction of the signal from one side, turn the disc upside down and load the disc into the apparatus again for the reproduction of the signals from the other side. Accordingly, this procedure involves the problem of being very cumbersome.
On the other hand, a device has been proposed which is adapted to reproduce the signal continuously without turning the disc upside down (Unexamined Japanese patent application SHO 57-169936). With reference to FIG. 38, this device comprises transport means 164 having a rotary mechanism 162 and a feed mechanism 163, a crank arm 161 mounted on the transport means 164, and a signal reproducing pickup 160 attached to the forward end of the arm. With the device, an optical disc 10 is rotated at a high speed by a spindle motor 21, and the feed mechanism 163 operates to move the pickup 160 from the inner periphery of the disc toward its outer periphery radially thereof for the signal reproduction from one side of the disc. When the pickup 160 reaches the outer periphery, the rotary mechanism 162 operates to rotate the crank arm 161 through 180 degrees, whereby the pickup 160 is inverted to a position opposed to the other side of the disc. The pickup is thereafter moved from the disc outer periphery toward the inner periphery for signal reproduction. Thus, the signal can be reproduced from opposite sides of the disc continuously by the single pickup.
The pickup has an extremely exquisite sensor structure, for example, of the mechanical type, electric type or optical type including a semiconductor laser. In the case of the optical type, the distance between the disc record face and the pickup is about 2 mm, and this distance is maintained within a variation range of .+-.1.5 micrometers during reproduction.
To assure the optical disc apparatus of signal reproduction with high fidelity, the pickup must perform a tracking operation with high precision, so that the pickup must be movable accurately along a radial line of the disc while being maintained at a predetermined level. With the conventional device described above, the transport means 164 comprises two drive mechanisms, i.e. the rotary mechanism 162 and the feed mechanism 163, which are different in the mode of operation and connected together, and the pickup is so supported as to be reciprocatingly movable and also rotatable. The increased freedom of movement given to the pickup invariably impairs the precision with which the pickup is positioned. It is extremely difficult to accurately position the pickup on the radial line of the disc by the inversion of the crank arm.
Further with the conventional device, the influence of the deflection of the pickup in the circumferential direction of the disc may be precluded by electrical processing, whereas variations in the distance between the pickup and the disc record face could lead to errors in reproduction tracking. Especially when reproducing signals from both sides of the disc, the pickup must be held at the specified level from the record face on each disc side with high precision, whereas the conventional device fails to afford such high precision.